In the typical manufacturing process for read/write heads for magnetic storage devices, a large number of sliders are fabricated from a single wafer having rows and columns of the magnetic transducers that are deposited simultaneously on a wafer surface using semiconductor-type process methods. In various process embodiments, further processing occurs after the wafer is sliced into quadrants and/or rows. In one embodiment the rows of magnetic heads are attached to a carrier with the transducers facing upward. The rows are then processed to form the air-bearing surface features and protective layers. Typically, a slider is formed with an aerodynamic pattern of protrusions (air-bearing features) on the air-bearing surface (ABS) which enable the slider to fly at a constant height close to the disk during operation of the disk drive. The recording density of a magnetic disk drive is limited by the distance between a transducer and the magnetic media. One goal of air-bearing slider design is to “fly” as closely as possible to the magnetic medium while avoiding excessive physical impact with the medium. Smaller spacing or “fly height” is desired so that the transducer can distinguish between the magnetic fields emanating from closely spaced regions on the disk. For more complex ABS patterns with multiple step levels, the lithography steps may be repeated. After all of the features have been formed, the row bars are separated with a diamond-cut saw into individual sliders, each having a magnetic head terminating at the ABS. It should be noted that the sliders are processed at the row level as a manufacturing convenience and that the sliders may also be cut from the row before processing.
Photolithography can be used in the process of forming the air-bearing features. Photoresist material comes in both liquid and dry forms. Either type of resist is applied and then exposed through a mask under high intensity light. In the liquid resist case the structure is then baked to stabilize the resist and to remove any residual solvent. In one process used by the applicants the exposed liquid resist is baked for approximately 30 minutes at about 100 degrees C. After exposure, the process of developing the image (positive or negative) in the photoresist removes the unwanted photoresist.
One method of forming air-bearing features uses a photoresist in conjunction with ion milling. The resist is exposed and developed to form a resist pattern covering the regions on the surface for the features (such as side-rails and the center rail) which will become the air-bearing features of the slider. The regions not covered by the resist pattern are etched by ion milling to form the features which protrude above the rest of the ABS surface. The resist pattern is then removed. A particular embodiment of a method for forming air-bearing features is described in U.S. Pat. No. 6,529,346 to Otsuka. A resist is applied on a carbon film that has been deposited over the surfaces of the transducers before the ion milling step.
In U.S. Pat. No. 6,503,406 to Hsiao, et al. the use of a temporary protective layer is described to prevent damage during the ABS patterning. During the etching process, the unmasked portion of the temporary protective coating is removed first, and the underlying area of the slider is then removed to a depth which is chosen to provide the desired flying characteristics for the slider. The remainder of the photoresist mask is then removed by a suitable solvent or by a soda blast.
In U.S. Pat. No. 6,322,431 Schaenzer, et al. ion milling of the photoresist patterned surface of burnishing heads is used to form surface features useful for burnishing. Burnishing heads contain no magnetic transducers.
In U.S. Pat. No. 6,411,478 to Mao, et al., a potential problem with the use of photoresist present during the formation of the tunnel barrier in a spin tunnel magnetic transducer is noted. The out-gasing from the photoresist is said to pollute the barrier material and degrade the barrier quality. To remedy this potential problem, a hard mask is suggested as a replacement for, or in addition to, the photoresist.
Applicants have found that the prior art methods using ion milling to form ABS features result in variations in the depth of material removed that are undesirable. Thus, there is a need for methods which reduce the variations in the depth of material removed by ion milling.